JPH021178B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a rubber composition for tire tread in a pneumatic tire, and by using a rubber composition containing a new polyisoprene rubber, it is possible to improve low rolling properties, wet skid properties, abrasion resistance, and handling stability. The present invention aims to provide a pneumatic tire that simultaneously significantly improves cut resistance and has well-balanced characteristics. There is a strong social demand for resource conservation.
There is an extremely strong desire to conserve resources, not only for the automobile itself, but also for tires, which are a component of the automobile. As a measure to save resources in tires, there is an idea of reducing weight and reducing rolling resistance, but in this invention, in addition to reducing rolling resistance, consideration is also given to the balance with other tire characteristics. be. It is known that the tread is the part that has the greatest influence on the rolling resistance of a tire, with an influence rate of nearly 50%. This rolling resistance is due to energy loss in the material due to repeated deformation as the tire rotates while running. In addition to the above-mentioned low rolling resistance, the tread portion is also required to have wet skidding properties, wear resistance, handling stability, and cut resistance. Conventional passenger car tires have been composed of rubber compositions such as SBR or SBR blended with small amounts of other rubbers. This commonly used rubber composition has a high rolling resistance, and if the type and amount of carbon black or the amount of sulfur or the like is changed in order to lower this resistance, other properties deteriorate and are unsatisfactory. This invention seeks to find a tire composition that fully satisfies these five characteristics. In other words, in general, when a tire is made to have a low fuel consumption tread, that is, a tread with low rolling resistance, its wear resistance, cut resistance, and handling stability also deteriorate. However, the present invention aims to improve fuel efficiency and at the same time to improve the above-mentioned disadvantages, and achieves this objective by changing the type of rubber. That is, as a rubber composition, a new polyisoprene rubber that has been given characteristics by changing the bonding state in the polyisoprene rubber may be used alone, or a combination of the polyisoprene rubber, natural rubber, and/or other diene-based synthetic rubber. It is characterized by being used in combination with one or more types of polymers. Generally commercially available polyisoprene rubber, such as polyisoprene rubber IR manufactured by Japan Synthetic Rubber Co., Ltd.
-2200 has 98% cis-1,4-bonds and trans-
The proportion of 1,4-bonds is 1% and that of 3,4-bonds is 1%. In this invention, unlike conventional polyisoprene rubber, 1,2-bond and 3,
4-By selecting a specific range of rubbers with a high total bond content, it is possible to combine them alone or with natural rubber and/or
Or by blending with other diene-based synthetic rubbers, the difference between the rebound value at a temperature of 60℃ and the rebound value at a temperature of 23℃ is 20 or more, resulting in low rolling properties, wet skid properties, wear resistance, and handling properties. A rubber composition for tire tread with well-balanced stability and cut resistance was obtained. 1,2-bonds and 3,4-bonds are in a form hanging from the main chain in the polymer, and are thought to have the same effect on each of the above items, so the sum of both is the value for each item. We investigated the impact it has on In addition, in the polymerization reaction, 3,4-bonds are more easily formed than 1,2-bonds. As a result of the above investigation, the X value of the total content (%) of 1,2-bonds and 3,4-bonds, that is, the X value (%) = 1,2-bond amount (%) + 3,4-bond amount (%), the fuel efficiency is not much different from conventional polyisoprene rubber that contains a high proportion of CiS-1,4-bonds until the tends to worsen,
It has been found that wet skidding properties, cut resistance, and handling stability tend to improve as the X value increases. It has also been found that wear resistance deteriorates rapidly when the X value exceeds 60. That is, the X value is first 60 or less, and on the other hand, if the X value is less than 20, the cut resistance deteriorates rapidly, so it is desirable that the X value is 20 or more. Emulsion-polymerized SBR has been the mainstream polymer commonly used in Toledo in the past, but the following comparative tests were conducted on this emulsion-polymerized SBR and the new polyisoprene rubber that is the subject of this invention. Regarding rolling resistance, it is known that the higher the rebound at high temperatures, the lower the rolling resistance, so the higher the Riyupke rebound value at 60°C, the better the fuel efficiency. It can be judged that it is good. In addition, regarding wear resistance, Rubber
Chemistry and Technology (RCT) Volume 34, 1
(1961), there is a high correlation between the Pico wear test and the tire actual running wear test, and if the Pico wear is good, the actual running wear is also good. . Also, regarding wet skid property, RC
As disclosed in the literature, Vol. 38, p. 840 (1965), using a portable wet skid tester manufactured by Stanley in the UK, the higher the test value, the more likely the rubber will be treaded in actual driving. It is said that tires with 100% wet skid properties have good wet skid properties, so we decided to compare them using this test value. In terms of the balance between wet skidding and rolling resistance, rolling resistance is 10 ² Hz,
Wet skidiness is said to be a phenomenon in different dimensions on the order of 10 ⁶ Hz.
If we consider this frequency in terms of temperature, approximately 1 order of Hz can be considered to be approximately 10 degrees Celsius, so
The difference between 10 ⁶ Hz and 10 ² Hz above is considered to be a temperature difference of 40°C. Considering this in terms of temperature dependence in rebound, assuming rolling resistance is approximately 60℃,
Wet skid property is considered to correspond to the rebound value at around 20°C, which is 40°C lower, and a good balance between these two means that the rebound value is low at around 20°C and high at 60°C. considered to be a thing. In other words, the greater the temperature dependence within this range, the better. Tables 1 and 2 show the results of comparative tests conducted on 185/70HR14 tires using tire compositions of various formulations in the tread area. Regarding rolling resistance, rolling resistance, that is, rolling resistance, was measured on a 60-inch diameter drum at an air pressure of 1.9 kg/cm ² , a load of 300 kg on the tire, and a speed of 60 km/h. Regarding steering stability, the same tires as those used in the rolling resistance measurement above were mounted on a vehicle and a running test was conducted at 80 km/h, and the feeling was measured and expressed as an index. A large index indicates good steering stability. Regarding cut resistance, cutter with a load of 5 kg is
It is made to fall freely from 60 cm, the depth of penetration into the rubber is measured, and the degree of resistance is compared with an index.
The larger the index, the shallower the penetration depth and the better the cut resistance. Table 1 compares emulsion polymerized SBR (SBR-1502), which has conventionally been widely used for tread rubber, with examples in which the microstructure of polyisoprene rubber, which is the object of this invention, is changed in various ways. It is something that In addition, as reference data
Synthetic isoprene rubber IR with many cis-1,4-bonds
-2200 (manufactured by Nippon Zeon) is also shown. The rubber compounding composition is as follows. Polymer 100 (parts by weight) ZnO 3.0 Stearic acid 2.5 Wax 2.0 Anti-aging 2.0 Carbon black N-339 45 Aromatic oil 5.0 Accelerator D 0.2 Accelerator MSA 1.5 Sulfur 2.0 Table 2 also shows the document No. in Table 1. 3 polymers were selected, natural rubber NR, emulsion polymerization SBR
(SBR1502) and SBR with a high content of 1,2 bonds of butadiene, so-called vinyl SBR, were tested for their properties.Other general blends are shown in relation to Table 1. is the same as

【table】

[Table] As shown in Table 1, the microstructure of polyisoprene rubber is the sum of 1,2-bonds and 3,4-bonds
(%), the following results were obtained when comparing polymers with various changes in the range of 15 to 66 with conventional polymers. Sample No. 1...X value 15 The wet skid property showed the same value as SBR1502, but the cut resistance was inferior to SBR1502. Sample No. 2...X value 25 Sample No. 3...X value 35 Sample No. 4...X value 44 The rebound at 60℃ is also higher than SBR1502, and the rebound value at 60℃ and the rebound value at 23℃ (abbreviation Reb.60℃－Reb.23℃)
is 20 or more, and has a good balance between rolling resistance and wet skidding properties. The wet skid values also show good values of 51, 53, and 54, respectively. In terms of wear resistance, it shows approximately the same value as SBR1502, and also has handling stability, cut resistance, and rolling resistance.
Better than SBR1502. Sample No. 5: X value 66 The wet skidding properties, steering stability, and cut resistance were generally good, but the abrasion resistance was extremely poor, making it unsuitable as a tire tread composition. From the above test results, it has been found that unless the X value is in the range of 20 to 60, it is not possible to achieve a balance among the five characteristics. In addition, in Table 2, sample No. 3 with an X value of 35 is selected as a representative sample with an X value in the range of 20 to 60, and NR,
When we tested the mutual properties of blend systems with SBR1502 and vinyl SBR, we obtained the following results. Blend Nos. B1 to B4 show blend systems with SBR1502, but the blending example of B1 is Reb,
60℃-Reb, 23℃ is slightly better at 14,
It cannot be considered that the balance between rolling resistance and wet skidding property has been sufficiently improved. However, when 40 parts by weight or more of this new polyisoprene is used, it is considered that the above five properties are sufficiently balanced. B5 is made of new polyisoprene rubber and NR.
B6 was tested as a ternary blend system with SBR1502, and B6 was a ternary blend system of new polyisoprene rubber, NR, and vinyl SBR. The results were shown. Therefore, 30% by weight or more of new polyisoprene rubber and natural rubber and/or
It was also confirmed that a polymer blend with 70% by weight or less of one or more other diene-based synthetic rubbers is also effective.

Claims (1)

[Claims] 1 X of the total content (%) of 1,2-bond and 3,4-bond structures in synthetic isoprene rubber
A polyisoprene rubber alone or a polymer containing 30% by weight or more of the polyisoprene rubber and one or more types of natural rubber and/or other diene-based synthetic rubbers having a microstructure with a value of 20% to 60%.
A rubber composition for tire tread comprising a polymer blend of 70% by weight or less.